Process of making nitrates and nitric acid.



0. SCHNHBRR & J. BRODE.`

PROCESS oP MAKING NITRATBS AND NITRIG ACID.

APPLICATION FILED JAN.29,1910.

1,039,325, Patented Sept.24,1912.

UNITED sTATEs PATENT oEEioE.

NORWAY, ASSIGNORS, BY MESNE ASSIGNMENTS, T NORSVK HYDRO-ELEKTRISKKVAELSTOFAKTIESELSKAB, 0F CHRISTIANIA, NORWAY.

PROCESS-OF MAKING NITBATES AND NITRIC ACID,

Specification of Letters Patent.

Patented Sept. 24, 19.12.

To all 'wkomz't may concern Be it known that we,O'rro SCHNHERR, Ph. D.,and JoHANNEs BRoDE,\Ph. D., chemists, subjects, respectivel of the Kin'of Saxony and the King o Prussia, resi ing, respectively, atChristiania and Christ1ansand, Norway, have invented new and usefulImprovements in Processes of Making Nitrates and Nitric Acid, of whichthe following is a specification.

Our invention relates to the production of nitrates.

It has long been known that nitrates are formed and nitrous fumes areevolved when nitrites are treated with nitric acid. The specification ofBritish Letters Patent No. 28,614 A. D. 1904 describes a process ,forthe production of pure nitrates from 'a mixture of nitrites andnitrates, by treating such mixture with nitric acid (preferably Whileboiling) and absorbing, by means of the alkalis, earth alkalis, or theircarbonates, the gases which are 4given 0E. This rocess requires theseparate production o nitric acid to act on the mixture of nitrates andnitrites.

We have found that we can produce commercially pure nitrates fromnitrites (whether free from, or in admixture with, nitrates) in a muchmore advantageous manner by acting: on such nitrites with nitric acid,then adding to lthe gases which are evolved so much oxygen (either assuch or in gases containing free oxygen, such as atmospheric air, orpreferably gases which are obtained by passing air through an electricdischarge) that the atomic proportion of total oxygen present is, to thequantity of combined nitrogen, as 5 is to 2,01- thereabout, or at anyrate so that no very great excess of oxygen is present, and thensubjecting these gases to theabsorbing action of water, or absorbingagent containing water but containing no basic compound. In this wanitric acid is obtained and this, or a part t iereof, can be used in thefurther treatment of a'fresh quantity of nitrite. The gases which areobtained by treat-in nitrites with nitric acid, on being mixe withsuchquantities of oxygen, or oxygencontaining gases as aforesaid, containsuch proportion of the higher oxids of nitrogen that their absorptionrequires comparatively small apparatus. The use of the gases obtained bytreating air in an electrlc arc is particularly advantageous whencarrying out our process, because the quantity of nitrogen oxidscontained in such `gases is thereby raised from about two per cent. toconsiderably above this, and consequently the absorption proceeds muchbetter. Even if only so much of the nitrous gases be absorbed that twoper cent. remain in them when they leavethe acid absorbing apparatus(that is, the apparatus in which Ithe gases are treated with water, orwith a lnon-alkaline aqueous solution, and in which nitric acid isroduced), and enter the a paratus where t e are treated with alkalinecompounds (t at is, the apparatus in which nitrite, or a mixture ofnitrate and nitrite, is produced), the whole of the nitric acid whichhas beenI added to the nitrite is regenerated as such, and consequentlthe conditions are such as are necessary or a continuous process. If,however, the absorption be carried out so that less than two per cent.of nitrous gases remain in the gaseous mixture leaving the acidabsorbing ap aratus, an excess of nit-ric acid is obtained). A furtheradvantage of the process accordi'n to our invention is that dilutenitric aci whereas by the absorption of the gases evolved it isdpossible to obtain a solution of nitric aci containing sixty-three percent. of pure acid, that is, a fairly concen instead of the nitric acidalone. Such mixture of nitric acid with a solution of nitrate isobtained. for example, when nitrous gases are absorbed in a solution dofnitrate instead of in pure water. This modification of the process isuseful when working on a ycanbe used for the treatment'of nitrites,

apparatus.

largescale, because av portion -of the nitrate solution obtained can beemployed for the absorption of the nitrous gases, and then, when itcontains suicient nitric acid, it can be added to the nitrites,whereupon the nitrites are converted into nitrates* and a morelconcentrated solution of nitrates isobtained. As a rule the gasesobtained by treating a solution of a nitrite with nitric acid containnitric oxid (NO) and very little, or no, other oxid of nitrogen. y Insome cases, however, for instance when lime has been used for theproduction of the nitrite, it is difficulty to avoid some carbonatebecoming mixed with t-he nitrite and consequent-1y when the nitritesolution is treated with nitric-acid thenitric oxid evolved containssome carbon dioxid. It is diiiicult to ,separatel carbon 'dioxidfromnitrogen t-rioxid and nitrogen peroxid so that in order to be able toproduce nitratesI and. nitrites free from carbonates we bring the gasesevolved on treating the nitrite with nitric acid and which containprincipally nit-ric oxid, into contact with a suitable alkalinesubstance before adding any oxygen to them. By this means, the carbondioxid is absorbed, while the nitric oxid is unaffected and can besubsequently treated with oxygen in any desired manner as aforesaid, andthen be subjected to the action of the non-alkaline aqueous absorbent soas 'to effect the absorption of the higher oxids of nitrogen thusformed,

The suitable alkaline substance can be" employed in a solid, or in adissolved state, or

'in the form of a suspension such for inst-ance as milk of lime. l

The process can be carried out in any suitable kind of apparatus, and,if desired, the different steps of the operation, or sev-y eral of them,can be carried out in the same For instance, the nitrous gases set freecan, after' being mixed with the requisite amount of oxygen, be causedto act on the nitrite in the saine apparatusl in which the saidgaseswere evolved. In this case, the quantity of nitric acid originally`added to the nitrite can be less than that theoretically required toconvert t-he nitrite into nitrate. The process should be so carried outthat the gases come as thoroughly as possible into contact with thesolution containing the nitrite, and for this purpose we vprefer to makeuse of towers through which the gases are passed and down which thesolution of nitrite is allowed to trickle.

A modification of this process consists in acting on a solution of anitrite or a solution containing nitrite andnitrate with nitric acid,allowing the' gases evolved (containing oxids of nitrogeniyto mix withoxygen, then causing the higher-oxids of nitrogen formed to be absorbedby means of Water or a nonalkaline aqueous absorbent, and thenimmediately allowing the nitric acid thus formed to react on afreshquantity of ysolution-containing nitrite, at the Sametime allowinga small excess of acid to take part in the reaction. -This modificationis of particular advantage, sincev if the quantity of nitrite containedin the solution being treated should vary, for instance diminish, thequantity of oxids of nitrogen evolved will be smaller and consequentlythe amount of nitric acid returning to act onthe new solution of nitritealso diminishes. .In this way the accumulation of a large excess ofnitric acid is avoided. In a' similar manner, if a solution which isstronger in nitrite be employed, after a short time the absolutequantity of nitric acid being returned from the absorber increases inproportion, consequently the process adapts itself automatically to theconditions obtaining. `This particular modification can for instance becarried out by allowing the nitric acid which is being returned from'theabsorber to mixwith the solution containing nitrite in a mixing vesseland at the same time allowing the small excess of nitric acid, which ispreferably added in order to make sure that all the nitrite isdecomposed, to run into the vessel. A current of gas containing. freeoxygen, for instance air, is passed in suitable `quantity through theIsaid mixing vessel,

being introduced at or near the bottom thereof. A solution of nitratecan be run ofl1 continuously from the mixing vessel.

The small quantity of excess acid aforesaid can eitherv be addeddirectly, or it can be actually formed in the mixing vessel bypassinginto the Vessel gases containing oxyids of nitrogen, such for'instance as those keeping theliquid in motion, and we have l found thatit is particularly advantageous to allow the solution to run down towers`which are kept .under negative pressure.

This removal of nitrous acid can of course .be carried out continuously,the solution to be treated being .run into-thej vessel while ai'continuous stream of liquid which has:

been freed from nitrous `acid is.- taken away from the vessel. Forinstance a solution` of nitrate containing nitrous acid such as isobtained by treat-ing a solution of nitrite and nitrate with nitricacid, is drawn into a tower which is kept under a considerable negativepressure. While the liquid is in the tube leading to the tower or in thetower itself, nitric oxid is evolved and should be drawn away by meansof a vacuum pump, which is preferably kept alkaline, while the solutionwhich has been freed from nitrous acid runs from the tower down a longpipe which is so arranged that the weight of the liquid in this pipecorresponds to the difference between the atmospheric pressure andthepressure in the tower.

The vacuum pump can be maintained alkaline by any ofthe well knownmethods, for instance milk of lime may besprayed into the cylinder onthe suction side of the piston, or a layer of milk of lime may be keptpermanently interposed between the piston and the gases which arey beingpumped, the cylinder in this case being situated vertically.

The process of our invention is particularly useful for the productionof pure nitrates from mixtures of nitrates and nitrites, because suchmixtures are generally' obtained during the absorption of nitrous gasesby an alkaline absorbing agent, such sodium' carbonate, milk of lime,and the 1 e.

,l ln order that the invention may be better. understood, reference maybe had to the accompanying drawing which illustrates diagrammaticallythe several steps of a cyclical process embodying the invention, but Wedo not wish vto be understood as restricting our invention to anythingshown in the drawing.

`Now what we claim is 1. The process of producing nitrate and nitricacid by treating a nitrite with nitric acid, adding a limited quantityof oxygen to t-he gas which is evolved during said treatment, and thensubjecting the gaseous mixture so obtained to the action of Water.

2. The process of producing nitrate and nitric acid by treating amixture of nitrite and nitrate with nitric acid, adding a limitedquantity of oxygen to the gas which is evolved during said treatment,and then 50 subjecting the gaseous mixture so obtained to the action ofwater.

3.' The process of producing nitrate by treating a mixture of nitriteand nitrate with nitric acid, adding a limited quantity 55 of a gascontaining free oxygen to the gas which is evolved during saidtreatment, and then subjecting the gaseous mixture so obtained to theaction of Water.

' 4. The process of producing nitrate and 60 nitric acid by treating amixture of nitrite and nitrate with nitric acid, adding a limitedquantity of a gas containing ree oxygen to the gas which is evolvedduring said treatment and then subjecting the gaseous 35 mixture soobtained to the action of an absorbing agent containing water hutcontaining no basic compound.

5. rlhe process of producing nitrate and nitric acid by treating anitrite with nitric acid, then purifying the gases evolved by' Tobringing them into cowact with a suitable alkaline reagent for thepurpose of absorbing carbon dioxid from the said gases, then adding alimited quantity of oxygen to the residual gas, and then subjecting thewhole gaseous mixture to the action of water.

t3. The process of producing nitrate and nitric acid by treating amixture oi' nitrite and nitrate with nitric acid, then urifying thegases evolved by bringing t em `into contact with a suitable alkalinereagent for the purpose of absorbing carbon dioxid from the said gases,then adding a limited quantity of oxygen to the residual gas, and thensubjecting the whole gaseous mixture to the action of water.'

7. The process of producing nitrate and nitric acid by treating amixture of nitrite and nitrate with nitric acid, then purifying thegases evolved by bringing them into contact with a suitable alkalinereagent for the purpose of absorbing carbon dioxid from the said gases,then adding a limited quantity of a as containing free oxygen to the gaswhich is evolved during said treatment, and then subjecting the gaseousmixture so obtained to the action of water.

8. The process of producing nitrate and nitric acid by treating amixture of nitrite and nitrate with nitric acid, then urifying the gasesevolved by bringing t em into contact with a suitable alkaline reagentfor the purpose of absorbing carbon dioxid from the said gases, adding alimited quantity of a gas containing free oxygen vto the gas which isevolved during said treatment and then subjecting the gaseous mixture soobtained to the action'of an absorbing agent containing water. butcontaining no basic compound.

9. The recess of producing nitrate and nitric acidp by treating anitritewith nitric acid, adding a limited quantity of oxygen to the gaswhich is evolved during such treatment, and then subjecting the gaseousmixture so obtained to the absorbing action of the aqueous liquidproduced by the treatment of the said nitrite with the said nitric acid.

10. The process of producing nitrate` and nitric acid by treating anitrite with nitrlc acid, then purifying the gases evolved by bringingthem into contact with a sultable alkaline reagent for the purpose ofabsorbing carbon dioxid from the said gases, then adding a limitedquantity of oxygen to 'the residual gas, and then subjecting the wholegaseous mixture to the action ofthe aqueous liquid produced by thetreatment of the said nitrite with the said nitric acid.

11. The process of producing nitrate by treating a nitrite withnitricacid, allowing the gases evolved, which contain nitric oXid, tomix with free oxygen, then causing the higher oXids of nitrogen formedto be absorbed by means of water, and then `allowing the nitric acidthus formed to react on a fresh `quantity ofnitrite, and at the sametime adding a small quantity of excess'nitric acid to take part intheireaction.

12. yThe process of producing nitrate by treating a'solution of anitrite with nitric acid,l allowing the gases evolved, which containnitric oxid, to mix with free oxygen, then causing .the higher oxids ofnitrogen formed to be absorbed by means of water, then allowing thenitric acid thus formed to react on a fresh quantityV of solution ofnitrite, and at the same time adding a small excessof nitric acid tothelreaction mixture.

13. The process of producing nitrate continuously by treating a solutionofl a nitrite with nitric acid, which process consists in adding freeoxygen to the oXids of nitrogen which are evolved during such treatment,then causing the higher oXids of' nitrogen which are thus formed to beabsorbed by means of water, then allowing the nitric acid vthus producedto react on a nfresh' quantity ofV a solution of nitrite.

14. The process of producing nitrate conf Linuously by treating asolution of a nitrite with nitric acid, which process consists 1n addingfree oxygen to the oXids of'nitrogen which vare evolved duringfsuchtreatment, then causing the higher oxids ofnitrogen which are thusformed to be absorbed by means of water, then allowing" the -nitrlc acidthus produced to react on a fresh quantity of a solution of nitrite, andalso 40 continuously adding a small excess of nitric acid to thereaction mixture.

In `testimony whereof we have hereunto set our 4hands in the presence oftwo subscribing witnesses.

- OTTO SCHNHERR. JOHANNES BRODE.

l/Vitnesses to the signature of Otto Schnherr:

HENRY BONLAMIAH. M. GULLORMSON. Witnesses to the signature of JohannesBrodo:

AUGUST GErrz, SOEBRE ULGHRIN.

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